The present invention relates to an optical scanning device including optical elements such as mirrors and lenses that constitute respective light paths for light beams emitted from a plurality of light sources, and to an electrophotography type image forming apparatus such as a printer including a plurality of latent image carriers that are exposed to the light from the optical scanning device.
The image forming apparatus that performs an electrophotographic image formation process is equipped with the optical scanning device that scans and exposes a photoconductor as a latent image carrier to be scanned with image light. The optical scanning device includes a light source, a scanning portion, and optical elements. The light source emits the image light modulated by image data. The scanning portion scans the photoconductor with the image light as a light beam in a main scanning direction. The optical elements include lenses and mirrors. The optical scanning device is housed in a light blocking enclosure for preventing influence of external light. The image light is distributed to the photoconductor through a window formed in a part of the enclosure.
Some of such optical scanning devices include a plurality of light sources. For instance, an optical scanning device that is used for a color image forming apparatus includes at least four light sources for emitting yellow, magenta, cyan, and black color image light beams. The optical scanning device that is used for the color image forming apparatus forms respective light paths for leading light beams emitted from the four light sources to four photoconductors of the color image forming apparatus, respectively. In order to reduce the number of components for reducing size and cost, the light beams emitted from four light sources are scanned by a single scanning portion.
However, in order to deflect a plurality of image light beams by a single scanning portion, the image light beams must be close to each other. Therefore, an image light beam may be reflected by an inner surface of the enclosure or a component to be stray light entering the light path of another image light. For instance, if magenta stray light enters the light path of yellow image light, the magenta stray light is distributed together with the yellow image light to the photoconductor so that undesired exposure is performed. As a result, a yellow image cannot be written correctly on the photoconductor.
For this reason, there is a conventional optical scanning device, as disclosed in JP-A-H09-274134 for example, in which a flat plate disposed at periphery of a polygon mirror as the scanning portion is tilted so that an image light beam reflected by the flat plate does not enter the light path of another image light beam.
However, stray light is generated also in other parts than the flat plate disposed at periphery of the polygon mirror. Therefore, the structure described in JP-A-H09-274134 cannot securely prevent stray light from entering the light path of another image light.
In addition, in order to prevent generation of stray light, it is necessary to specify a part generating stray light so as to stick a low reflection member to the part generating stray light or to adjust the angle. However, it is not easy to specify the part generating stray light in the optical scanning device equipped with a single scanning portion, because a plurality of image light beams are deflected at the same timing.
An object of the present invention is to provide an optical scanning device and an image forming apparatus that can easily and securely prevent unnecessary exposure to stray light without necessity of specifying a part generating stray light or an adjustment with respect to the part generating stray light, by increasing light amount of the image light that is affected by the stray light and by decreasing light amount in the light path after stray light enter the same.